Posted
by
timothyon Sunday September 07, 2003 @02:45PM
from the and-half-the-fat dept.

fname writes "Here's a story from Spaceflight Now about a new test aircraft that can travel at supersonic speeds without triggering a sonic boom. The technology works by modifying the shape of the plane. Although it's been believed to be possible for a long time, this is the first actual flight test, barring black box projects I suppose."

Um, you mods are on crack. That's not flamebait, it's a paraphrased quote from a famous Warner Brothers cartoon featuring Marvin the Martian and Bugs Bunny entitled "Hare-Way to the Stars." The exchange in question goes like this:

Bugs Bunny: "Eh, pardon me, Doc. I've got to get back to the Earth."Marvin: "Oh, the Earth will be gone in just a few seconds. It obstructs my view of Venus."Bugs Bunny: "It does?! That's a shame."Marvin: "Where's the kaboom? There was supposed to be an Earth-shattering kaboo

Airplanes make plenty of noise even without the boom, so silience it isn't necessary. If it's enough to make supersonic flight over populated areas acceptable to people, the mission is accomplished. Noise is what really prevents supersonic passenger planes.

Noise is only a factor for intra-national flights. The real problem is fuel economy. Supersonic flight causes much more drag than subsonic flight. So even with a very well designed aircraft like the Concord, the amount of fuel per passanger-mile is about 3-4 times as much as for a Boeing 747.

At best, this will allow corporate execs to travel in small jets supersonically as they'll be the only ones who can afford it.

You only want to throw the thing out when maintaining it costs more than developing and buying a new one. While it might be hard to modify the concord's swiveling nose this way, it's worth looking into.

The next modification needed is to the law, so that flights that don't make too much noise can fly over the contenetal US. If you can get from New York to California supersonically, people will want to do it and will pay for the above mentioned development and building.

So, when can we throw out the Concord and whatnot and get transcontinental supersonic flight to boot?

For starters, you don't have to "throw out" the Concorde as BA/AF are doing that for you. They even refused to sell one to Virgin Airways as Branson might find a way to make the flight profitable and would thereby kill BA/AF's hopes of pushing all of the Concorde folks into the 747 first class section.

There are two other reasons why you won't see the Concorde flying supersonic over the continental USA, with or without a sonic boom:
1) There are far too many other slow aircraft flying at or near Concorde altitudes. Considering the fuel costs involved in getting to supersonic speeds (max drag between 0.97M and 1.4M), the economics of trans-continental supersonic flight would require sterile airspace for end-to-end clearance. The lobby group for bizjet owners would never let that happen at their expense.
2) Even a reduced shock wave will have destructive powers if the aircraft is required to turn at supersonic speeds - the waves on the inside of the turn are concentrated toward a single point at which the N-wave would be amplified to an unacceptable level. Although it would be possible to structure straight-line routes between city pairs, the odds are pretty good that the flight would be unmanageable in terms of communication and coordination among ATC units.

Other than exotics like the U2, what planes routinely fly at the 60000' cruise altitude of Concorde? Most planes I fly on cruise at about 35000'.

Well, the 767/777 routinely fly as high as 41,000'. Lear and Gulfstream both reach into the mid-50's.

Concorde didn't actually spend much time at 60,000. A typical trans-Atlantic flight would start at 45,000 and then slowly climb as fuel weight was reduced, with only the last hour of supersonic flight above 55,000'. In the first half of any transcontinental f

That's because you fly commercial like me, prole. OTOH, Gulfstreams and other long range bizjets cruise in the 50k' range. Check out 'specifications' at thus URL: http://www.gulfstream.com/g550/And while the Concorde ends its flight at 60K, it starts at 50 and gradually climbs as the weight of used fuel is lost. So not only is it ripping along at high speed but also constantly changing altitude. Not the kind of wild behavior you want over the continental US where there are a lot of the aforementioned bizjets puttering around at less than half the speed.

Unfortunately, the article never reveals how much they have reduced the sonic boom.

But, this could be great for supersonic transports if the design technolgy is used in future designs. It would mean that we could have supersonic flights from NY to LA lasting only a couple hours! If the noise was reduced enough, the FAA would let them fly over populated areas (like the continental US)

I would really like more infomation on this, that article was incredibly short and left me with many questions. Mostly, how are the shock waves being broken up, and how would it affect the drag (ie, would it be a better design for watercraft also?)

But then again, it is a government project, can't expect much in the way of information.
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This was also covered in Flight International (subscribers - I read the paper version in the library), in a bit more depth. The classic sonic boom was described as "N-shaped" and gives a crack-crack effect. This modified it to more of a "table-top", and was said to sound like a long rumble.

Judging from the picture, the design borrows heavily from that of watercraft. The bottom of the aircraft has been modified to the point that it resembles the hull of a boat of personal watercraft.

I suspect that it works very similarly to the way that planing hulls(no pun intended) work. Just as a boat's hull spreads its wake outwards from the sides of the hull, this aircraft design likely spreads the aircraft's wake out to the sides more than straight down. This would reduce the pressure wave below the aircraft. I am confident that if the sonic boom was measured from the side on the same plane with the aircrafts altitude the sonic boom would be the same as normal and possibly more intense.

Judging from the picture, the design borrows heavily from that of watercraft. The bottom of the aircraft has been modified to the point that it resembles the hull of a boat of personal watercraft.

Out of curiosity, does anyone know what speeds aircraft could see supercavitation at? I mean, given fluid dynamic apply to both air and water, shouldn't it be possible for planes as well as submarines? Anyone know what that would do to the shape/strength of a sonic boom?

you didn't mention the conspiracy theory though. Didn't you know that you have to post a link from the NYT, the Register, mention how Bill Gates is the anti-christ, or that there was some conspiracy going on?

Sure, but you only submitted one with links from NASA, the Pentagon, and a military contractor. I mean, if you aren't going to take the time to submit it with a real and reputable source linked, like Spaceflight Now, then how can we take you seriously?!?

Your submission is more informative, but honestly, my bet is it was rejected because you went overboard on your links. For example, you had 3 different links on the F5E, when one would have more than sufficed. I think the article that was actually accepted is on the opposite extreme of the spectrum (one link?), but with your's, you have to play the "Guess which one's the story that you actually want to read" game.
Note, this isn't a flame. I'm just trying to give you constructive criticism that might help

That's why I don't won't to submit anything to/. anymore - they approve badly written, "grammer-prone" dupes from their friends, but never from unknown people, even if submitted material were good for reading.

It doesn't matter, a geek forum or a fortune-500. People are the same. They love their friends. No matter that it may sacrafice the quality of their business.

That is differnt. It is for a single shockwave. What this article deals with is multiple shockwaves.

The examples are ATF, Eurofighter, Viggen, Suhoy S27 and later, so on so forth. All of these have shapes designed specifically to split the shockwave into a series of shockwaves to improve lift and maneuvrability at hypersonic speeds. As a result the noise is muffled as a side effect. From there to muffling it completely is just one step.

In btw, I am glad that it was done on the F5. It is the only US bird that has some resemblance of grace and beauty in the air.

I believe it's possible to eliminate the major side effect of a sonic boom, to the point that in lay parlance we will have aircraft that do not generate a sonic boom.

If you can manipulate the shockwaves and bowfronts trailing a plane in such a way that they interfere, essentially producing low energy zones at the appropriate distance, and then redirect the rest of the sonic energy to disperse and spread out along a larger surface area and upwards into empty space, you can create supersonic craft with subso

The future of ultra fast transit isn't in airplanes gliding along, masking their sonic wake. It's with things like multi stage trans-orbital aircraft. A plane could take off using standard jets until it got to the maximum height the jets could support. Then switch over to SCRAM jets and break for the outer atmosphere. Even the prototype SCRAM jets today are capable of flying at many multiples of mach. It just takes the energy to get a plane beyond mach 2 (or so) to begin with. If you stay at the edge of the atmosphere, the very low pressures create little drag compared to today's cruising altitudes. Also, the higher you are, the faster you must go in order to create that critical pressure point. You don't need to totally leave the atmosphere; in fact it's easier that you don't. You won't have nearly as much heat to deal with as reentry, and you won't have to add rockets or thrusters to maneuver in low orbit. Imagine flying form New York to Tokyo so fast that food service isn't needed.

2) Well, according to the Northrop Grumman site [northgrum.com], they used sensors to measure the difference in loudness and they hoped that with further study, they could "produce a noticeably quieter sonic boom." Therefore, I'm guessing it wasn't reduced by a large factor, but the very fact that they *can* reduce it via aircraft design is rather significant.

It is LOUD. Its not like the long fading sound a subsonic jet creates, but a short "hit" of sound, like a gunshot, but with lower frequences.Thing of a bomb detonating 200 meters away or a single bass beat from love-parade class speakers inserted into silence.

A story i cannot verify is that in the early 80s a pair of tornados practives ultra low altitude "vallay crawling" and something went wrong.One pilot needed to gain altitude fast beca

"When you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of the meager and unsatisfactory kind."--Lord Kelvin

The article doesn't give one single blessed number that would enable anyone to judge how effective the experiment was.

I'm not sure what the right measurement would be... decibels? sones? psi? pascal-seconds? Or average blood pressure increase in human subjects in Hgmm? But the article doesn't say.

Not even the usual marketing claim, like "42% less boom than traditional aircraft, yet still has that same great NASA 'look'"

Something about "We were all blown away by the clarity of what we measured" just doesn't do it for me.

On the contrary, my guess is these low-noise jets will be even bigger gas guzzlers than normal supersonic jets, for three reasons.

1 - Fuel efficiency wasn't mentioned in the article. If it were better, I figure they'd be bragging about it.

2 - Apparantly the main advancement that they did was to have the air heat up near the nose of the aircraft, to make a smooth pressure gradient. Now that heating must come from friction, which takes energy (quite a bit when the air is rushing by at Mach 2).

3 - Current aircraft are designed with loads of computer aerodynamics modelling, with the main design goal being low drag (ie., high fuel efficiency), so if reducing the sonic boom reduced drag, it already would have been discovered and implemented long ago. In subsonic aircraft, design improvements of 0.01% are fairly typical and worth going after, as this is a very mature field of engineering.

I guess we can forget about those 4 hour NYC to Tokyo flights for the time being.

"Here's a story from Spaceflight Now about a new test aircraft that can travel at supersonic speeds [with a lessened sonic boom]. The technology works by modifying the shape of the [sonic boom]. Although it's been believed to be possible for a long time, this is the first actual flight test, barring black projects I suppose."

A reduced sonic boom has obvious civil purposes, but the aim of this program is to improve the designs of military aircraft. A reduced sonic boom would make supersonic aircraft in enemy airspace less noticeable.

Of course aircraft cannot be tracked using aural emissions, but it only takes sound to wake up an airbase full of sleeping pilots or snoozing radar operators...

This is simply the most amazing thing I have ever seen. A bunch of civi's were on a naval ship when a hotshot pilot buzzed the ship at supersonic speed. One of them happened to get some amazing video [rmwc.edu] of the pressure wave.

Supersonic vehicles actually generate two booms- one for the nose and one from the tail- that's why this has the nose glove and the modified tail.

Incidentally, the size of the boom is related to the size of the aircraft, military planes are much smaller and hence give much less problems.

Interestingly, Concorde's nose is sharp- this is aerodynamically efficient, but generates bad sonic booms- it would be much better to use a rounded nose from that respect. Detailed changes to the tail section (other than the ones shown here) can also greatly reduce the shockwave. If you've seen Thunderbirds, some of the airliners shown there are strongly reminiscent of the kinds of shapes that probably help out, (strangely enough, that's probably because they got fairly good advice when designing their models.)

I think that the vehicle shown in the photo has a compromise nose shape- it's sharp on top to give better aerodynamics, but rounded underneath to project a weaker sonic boom downwards. Atleast that's my take on what they've done- IANAA. (I Am Not An Aerodynamicist).

For those who have asked how much of a reduction in sonic boom was achieved:

The following URL says the peak pressure was reduced by one third, but there was very little difference in the sound of the boom on the ground. This was a better result than expected, since they did not expect to hear _any_ difference.

After all, this was _not_ an attempt to fly supersonically without generating a sonic boom, despite the misleading title of this thread. Instead, it was a (very successful) attempt to valid the CFD models used to design the aircraft nose modifications and predict the reduction of the pressure wave on the ground.

Now that they have proved that their method works, they can work on more noticeable reductions.

From the article:In flights conducted Aug. 27 on the same test range where Chuck Yeager first broke the sound barrier nearly 56 years ago...

Of course it works here. They admit themselves that the sound barrier is already broken at this location. Did anyone ever bother to FIX it in 56 years? Nooooooo. Maybe if it works at another location I will be impressed.

It makes it more practical to have supersonic travel in and around cities, which are notoriously noise sensitive. In the past, the routes for such planes were quite limited. Now, if the cost drops, perhaps we'll see them more in the mainstream.

Oh, and there are likely military applications, as well. Anything to reduce chances of someone hearing you coming can help (although, most times, these planes take off far from their mission).

A sonic boom isn't a one time deal when you crack the sound barrier. after you break it, the boom is continous as you fly over the ground. Thus if you travel supersonically over the entire width of texas, then the entire width of texas for that corridor your plane passes over will hear/feel the shockwave.

It is felt that the SST movement (i.e. concorde) was derailed by the american plane maker (i.e. Boeing) which got enough lawmakers to say that the concorde could not fly over the USA (i.e NY to LA) because of the sonic boom.

if a SST can go supersonic without the boom, then development of new craft could take place, because new markets could open up...

Uhh...no. Your story is refuted by the fact that the Russian program (which would have suffered none of the enivronmental concerns of the Boeing and Concorde efforts) failed as well, despite being hugely helped by data stolen from the Concorde's testing. The Russian SST died when their test plane crashed horribly at the Paris Air Show. Despite the Russian air fleet's total lack of interest in passenger safety, the Air Ministry decided to kill the project.

The big barrier to SST success has always been economics. It's incredibly expensive to fly faster than sound. Boeing had a quite successful SST program, but cancelled it when it became clear that SSTs would not be economical. Concorde never made money for either of its parent airlines, despite the incredibly expensive tickets for the flights for which it made any sense at all.

Your story is refuted by the fact that the Russian program (which would have suffered none of the enivronmental concerns of the Boeing and Concorde efforts) failed as wel

Your logic is refuted by the fact that Concorde was in service for almost 30 years -- it carried its first passengers in 1976. The technical failures of the Russian project have no bearing on Concorde.

in fact the original poster has a good point. Concorde failed to flourish economically largely because the US authorities refused it pe

No, not even close. Try
1954 [boeing.com]. I know I've seen on TV why they stopped but I cannot find the reason now. Fear of ballistic missiles or bombers doesn't fly (pardon the pun) since telling missiles bombers and civilian airplanes apart was the main reason there even is a NORAD. It was their main operational task. Even built huge analog machines, complete with PPI:s and light pens in the fifties to cope with the burden.

The Russian SST died when their test plane crashed horribly at the Paris Air Show.

That isn't what killed the TU-146. It was their inability to get modern digital fuel controls that doomed that plane. The engines were also used on a major Russian bomber and no way in hell did the West plan to help that program.

And, btw, what caused the SST crash at the Paris airshow was the TU-146 pilot having to suddenly dodge a French fighter plane that was playing hide-and-seek in the clouds trying to get some spy p

It is felt that the SST movement (i.e. concorde) was derailed by the american plane maker (i.e. Boeing) which got enough lawmakers to say that the concorde could not fly over the USA (i.e NY to LA) because of the sonic boom.

Getting 1/4 of the MPG per passenger compared to a subsonic plane also had something to do with it. The extra cost for fuel alone is going to double the price of most airline tickets.

That means you're in a niche market, which reduces the number of customers and impacts economy of scale. This increases maintenence costs and R&D and manufacturing overhead to very high levels. That's how you get $10,000 one-way fares across the Atlantic on the Concorde.

To compound the problem, most domestic flights just aren't that long. If you take a 1500-mile trip that needs a connection (as many do with the hub-and-spoke system), it can easily take you 9 hours to get from your home to your destination address, and only about 3 of those hours is in the air. An SST would cut that trip down to 7-1/2 or 8 hours at the cost of 4X the fuel usage. It just doesn't make any sense on the vast majority of flights.

People who would pay this price are already saving more time end-to-end than an SST airliner would save. They do it by flying private business jets on their own schedule between small airports which are uncongested and near their destinations.

supersonic aircraft are a pain. The concorde for example, stretches 11 inches while in flight - maintenance duties on them are expensive, as is the large amount of fuel they require.

On planes such as the 747, this is offset by the large load of passengers you can carry. In a supersonic jet however, you are limited by the shape of the plane. The concorde carries very few passengers as its fuselage is VERY narrow. At this point in time, its simply much too expensive to fly a fleet of supersonic passenger

This is important because the main reason super sonic airplanes are not used more often for civils is because of the sonic boom. The sonic booms can be very loud and disturbs urban areas. The Concord, for example, had to wait to be very far away from populated areas before getting into super sonic speeds. This rwas costly, since the Concord was design to have optimal fuel efficiency at super sonic speeds.

The Concorde was also removed from service because of its limited availability, due to ticket costs, its aging fleet, and its travelling through the Ozone layer. The first two would have to be fixed before SSTs became mainstream aircraft.

You're joking, right? the sonic boom from an aircraft can be ahelluva lot more than "loud." When I was a teen sharing a very rural house trailer we once experienced a "sonic boom" firsthand. Actually, it was TWO house trailers, joined at their middle by a "family room" type partition, forming an H-shaped structure. And when the boom happened, it made both trailers rock back and forth like a stick of dynamite had just gone off across the street.

Sonic booms can be a helluva lot more than just "loud" or "annoying." They can implode outbuildings, knock shit off shelves, break windows... and toss around house trailers like a blast from a hurricane.

1.) Military people can have fast jest (read "attack planes") that don't alert the person on the ground (read "those who aren't killed by the bomb that will be dropped on them") as to whether there is a jet above them.
2.) One of the biggest problems with commercial super-sonic airlines is that people didn't want them flying over their house (the major reason such flights were primarily only over the Atlantic Ocean). If the sonic boom didn't

The reason to do this is to allow supersonic transports to fly over inhabited areas. The sonic boom from the Concorde, for example, is shockingly loud, it would never be tolerated.

What the article doesn't say, but was reported in Aviation Week a few weeks ago, is that this technique (and certainly this airplane) only reduces sonic booms -- it doesn't eliminate them. This demonstration is to show people that the math is right; that the sonic booms can be reduced through shaping. It is still unclear whether it is possible to build a practical airplane with a tolerable (negligible) sonic boom. Perhaps this could be combined with other techniques (the Russians have been working with exciting a plasma in front of the airplane, for instance) and together you could get a minimal boom.

Probably the parent article was questioning the need for supersonic travel at all -- whether it's worth the cost. It will almost certainly be less fuel efficient than subsonic travel. Travel in general is less fuel efficient than staying home. Living is less fuel efficient than dying.

Not every technical advancement needs to be in better energy conversation. This will greatly help with noise pollution and lead to faster commercial plains in the future. Running a subsonic airplane will on the average will use less fuel then an supersonic one and supersonic plains will increase air pollution. But at least it is not making every bison in the midwest going deaf after a bunch of booms that break their eardrums. Sometimes the need for speed is more important then fuel consumption. (Think a

The Concords noise problems had more to do with takeoff and not supersonic flight.The engines that the Concord used where turbojets not the turbofans that airliners use now. To make matters worse the Concord used afterburners for take off. The amount of noise that that an afterburning tubojet makes compaired to tubofan of the same thurst is huge.To not make a sonic boom over land is easy. Just do not fly supersonic. THe trick is to make an engine that is efficent at supersonic and subsonic speeds and that d

I think it resembles one of those racing boats, the ones with jets on the back. Sort of like this: http://www.f1boat.com/02/portimao/images/ambiance/ flying_zepter.jpg
I suppose it make sense... so the plane can surf on the super-sonic shockwaves there by reducing their sound. I suppose simmilar wave physics are going on at super sonic speeds as they are at super-boat speeds.

A Naval Architect once told me that the speed of a boat is limited not by its motor so much as by it's hull length. This had somet

The airplanes displacement of air creates pressure waves. For a given velocity and displacement there is going to be a certain amount of energy and momentum that is transfered to the air. this is usually called sound and you can hear an feel it.

now under special conditions the sound waves all pile up making one giant pressure sheer, the shock front.

to the extent that you can disperse the shock front then the boom is indeed disperesed. You have not however eliminated the energy dumped into the air. But the "boom" is gone.

that's what this article is saying I beleive.

The really cool part of this is that its like to old adage about genius taking many steps. first everyone believes that something cannot be done. then some fool shows it might be not be impossible. then a scientist shows it is theoretically possible, and finally some engineer shows how to do it. Then it seems obvious

now that we have crossed the threshold of knowing that its possible to break the sound barrier without a sonic boom we can now get on with wondering if maybe the remaining waves could be modified in other ways, like directing all the sonic energy up and not down, minimizing it or maximally dispersing it. its now on the table.

It reminds me of discovery of negaitve index of refraction or of "optical bullets". At a certain optical power density the plasma of electrons stripped from air creates a non-linear lens that focuses a light beam in both time and space down to a stable optical pulse that neither diffracts nor diverges for macroscopic distances (hundred of meters till it runs out of energy). Now that is pretty weird since if you ask anyone who knows anything about light they will tell you that the two most fundamental proerties of waves propagation in media are dispersion and diffraction. Thus optical bullets are a form of electormagnetic farfield propagation that is not like a light wave. Negative index of refraction destroys another myth that light cant be focused smaller than a wavelength without non-linear methods.

so now we have yet another wave propagation myth falling, that when the speed of an aobject passes the wave speed in the media that a shock front is created.

just to go off on wacky extrapolation for a moment, I will point out that there is a close connection between the idea of a shock front and the idea that faster than light travel is impossible. Perhaps we can disperse that "light cone" and bend time some day.

now that we have crossed the threshold of knowing that its possible to break the sound barrier without a sonic boom we can now get on with wondering if maybe the remaining waves could be modified in other ways, like directing all the sonic energy up and not down, minimizing it or maximally dispersing it.

Or maybe modulating it? How much would Intel pay to have the sound pressure waves reproduce their jingle as the airplanes fly by?:-)